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U.S. Marine Reservist Andrew Tahmooressi was expected to testify before a Mexican judge Wednesday, the same judge who will ultimately determine his fate. NBC 7’s Sherene Tagharobi reports. (Published Wednesday, Jul 9, 2014)

Updated at 8:18 AM CST on Thursday, Jul 10, 2014

The fate of a U.S. Marine reservist jailed in Mexico for the past three months remained undecided Wednesday as he addressed a judge at an evidentiary hearing across the border.

Andrew Tahmooressi, 25, was expected to make a statement before a judge to explain the arrest that landed him behind bars in Mexico. Media was not allowed in the courtroom.

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Tahmooressi was arrested April 1 after driving his Ford pickup truck across the U.S.-Mexico border at San Ysidro into Tijuana. At the time, he was in possession of three U.S.-registered firearms and was arrested by Mexican officials and jailed on weapons charges.

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NBC 7's Danya Bacchus reports on the protest held Wednesday demanding that Mexico release U.S. Marine Andrew Tahmooressi who is being held on weapons charges. (Published Thursday, May 29, 2014)

The Marine reservist from Weston, Fla., was escorted by police in Tijuana to court Wednesday. Ultimately, his fate will be decided by a judge alone, not a jury.

Experts told NBC 7 the judge would review Tahmooressi’s testimony along with other evidence before making a decision on whether or not to set him free. That decision could take as long as four to 10 months.

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U.S. Marine Reservist Andrew Tahmooressi, jailed on a weapons charge, has been transferred to a safer prison, his mother tells NBC 7 Military Reporter Bridget Naso. (Published Monday, May 12, 2014)

Experts said Tahmooressi will likely remain behind bars for the duration of the trial.

San Diego-based attorney Jan Ronis, who’s familiar with this case and the Mexican justice system, believes the deciding factor will be the impression Tahmooressi makes on the judge.

“It’s going to be his credibility based upon his demeanor, his character, his reputation, because there’s no dispute that he went into Mexico. The dispute is did he do it intentionally and if so, why did he go to Mexico?” said Ronis.

In that letter, supporters urge the judge to consider that Tahmooressi was new to the area and unfamiliar with the border crossing. At the time of the incident Tahmooressi – who served two tours of duty in Afghanistan – was in the San Diego area to receive treatment for post-traumatic stress disorder (PTSD).

“I think it would be an easy decision for the judge, especially given some external pressures, to come to a decision that it was just an accident and let this man go,” Ronis told NBC 7. “On the other hand, the judge could find the evidence compelling that he entered the country intentionally with the intent to distribute weapons.”

Wednesday’s hearing was Tahmooressi’s opportunity to supplement the record with additional statements or perhaps modify earlier statements if they were incorrectly recorded.

An attorney subpoenaed two Mexican customs agents on duty at the time of Tahmooressi’s crossing and they’re expected to testify in the direct examination process as well.

As the evidence comes in and is reviewed by the judge, Ronis said the decision will inevitably take time. He said that would be the case even if Tahmooressi was jailed in the U.S.

“These things take long on both sides of the border. They are entitled to go through the process and nobody should really jump to conclusions about the fairness of the system until we see what the final decision is,” said Ronis.

“I think there’s ample evidence for [the judge] to believe it was purely an accident, that he did not enter Mexico intentionally with any intent to distribute weapons,” the attorney added.

"I hope that the judge will consider it and discern the truth and release Andrew," Tahmooressi told reporters at Fort Lauderdale-Hollywood International Airport Tuesday. "He's been just frighteningly abandoned for all these months and to have family present is definitely reassuring."